Tone control means



June 22,

1943. w. s. BAcHMAN 2 TONE CONTROL MEANS Filed Feb.. 19, 1942 Fi .1. 4,; I 5% TONE coumo; AT mo POSITION I 1 Tons co'umon. M

nmmun POSITION Inventor: William S. Bachman,

His thorn ey.

FREQUENCY Patented June 22,

UNITED STATES PATENT OFFICE.

N 'roNE-coN'raoL MEANS William S. Bachman, Fairfleld, Conn., assignor to General Electric Company, av corporation of New York Application February 19, 1942, Serial No. 431,587

' 7 Claims. ((1178-44) My invention relates to tone control means and more particularly to such means for effecting manual control of the high frequencies in the audio range? It has for one of its objects to provide improved means for controlling the high frequency response of an audio frequency system such as the audio amplifiers used in common household radio receivers,

Another object of my invention is to effect such means without materially increasing the cost of the system.

The novel features which I-believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof may best be' understood by reference to the following description taken in connection 'with the drawing in which Fig. 1 represents an embodiment of my invention: Figs. 2 and 3 represent certain modifications thereof, 'andFig. 4 represents certain characteristics pertaining to the invention.

Referring to Fig. 1 of the drawing, I have represented at I therein an electron'dis'charge device which maybe utilized, for example, as a detector and first audio frequency amplifier of a radio receiver. This discharge device comprises a cathode 2 and an anode 3. Signals of radio frequency to be detected may be supplied to a tuned circuit 4 connected between the anode 3 and the cathode 2 through the usual detector load resistance 5, which is shunted by the usual condenser 6. The circuit 4 may comprise, for example, the last tuned circuit in the intermediate frequency portion of a superhete'rodyne receiver, for example, upon which modulated currents of the intermediate frequency appear. These currents are rectified by the diode comstages of amplification and ultimately aloud speaker.

The intensity or volume of the current so amplified is controlled by variations of the slider 9 along the potentiometer I. To effectcontrol-of the amplification of the high frequency current with respect to the amplification of the low frequency currents, the path comprising resistancell, condenser l5, resistance I6 and condenser I1 is provided between the tap 9 and ground,'a variable point It on the resistance l6 being connected to the ungrpunded terminal of the resistance 5. I

prising electrodes 2 and 3 and the audio frequency potentials, which may be of voice or music frequencies, appear upon the resistance 5. Across this resistance is connected 9. volume control resistance I through the large coupling condenser l. A variable tap 9 on this resistor I is V connected throughcondenser III to the control electrode H of the discharge device i.

This controlelectrode is connected to the cathode of the discharge device by means of a resistance I2;

Thus voice or music currents appearingon resistance l are amplified in the amplification section of the discharge device I and appear upon the anode l3 and are supplied to any suitable load device, which may comprise additional When the tap It is at the top. or upper end of the resistance l6 as shown in the drawing. high frequency currents are supplied through the condenser l5 and resistance I4 to the tap 9 on resistance 1. Thushlgh frequencies are supplied directly to amplifier l without any atquencies to that at low is progressively increased.

When slider I8 is moved downward on resistance I6, this increased amplification is reduceci both by insertion of the upper portion of resistance it .in series with condenser l5 thereby reducing the extent to which high frequency cur rents are-supplied to contact 9, and also by reducing the portion of resistance It in series with condenser ll therebyincreasing the extent -to which high frequency currents are bypassed by that condenser. When contact it reaches the bottom of the resistance condenser H2 is com nected directly across resistance 5. When this occurs the response at high frequencies may be substantially nil.

Fig. :i represents, by way of example, certain frequency response characteristics obtained on a particular receiver having a tone control system such as that shown in Fig. l. The curves of the figure are plotted with the output of the receiver in decibels as ordinates and frequencyas abscissa The curve A of this'figure represents the response which exists when the tone control tap I8 is at the upper end of the resistance Ii. It will be seen that the response of the receiver is maximum at a frequency of, for example, 4,000 cycles, and is greater than at low frequencies. This curve corresponds to a condition in which the resistance I4 is omitted from the circuit. If resistance ll of desired value he inserted the response may be more nearly as indicated by the curve B. If the contact I 8 be moved downward on resistance IE to the mid-point, the frequency response curve may be then indicated .at C in which the high frequency response is shown as very greatly reduced with respect to that shown by curve A. If the tone control contact l8 be moved to the lower terminal of resistance IS, the response is as indicated by the curve D of Fig. 4 in which it will be seen 'that response at frequencies above 4,000 cycles is very small.

These surves of Fig. 4 apply when contact 9 on resistance 1 is at an intermediate point on that resistance. As contact 9 is moved downwardly on resistance 1 the effect of circuit l4, U5, IS in accentuating the high frequencies relative to the low frequencies is increased as the signal is reduced. Of course, the extent to which this increase occurs is dependent upon the values of the various circuit components employed. Dne set of values found satisfactory is as follows:

Resistance 1 =2 megohms Resistance l6 =2 megohms Resistance ll =180,000

Capacity 8=.005 microfarads Capacity l5=.0001 microfarads Capacity l'l =.005 microfarads Fig. 2 is substantially the same as that shown in Fig. 1 with the resistance I4 omitted. The signal source is represented in this figure at and as having internal resistance indicated at 20.

Fig. 3 differs from Fig. 2 in that the tone control network l5, l6, I1 is connected between a fixed point 2| on resistance I and ground- An additional network employed for bass compensation, comprising a resistance 22 and a condenser 23 in series, is also connected between this point 2| and ground. These latter elements are proportioned in the manner of the usual bass compensation network and by-pass a portion. of the I high frequency currents, thereby to increase the response at very low frequencies as, for example, frequencies below 400 cycles.

In this figure the effect of the bass compensation network 22, 23 and that portion of the tone control network comprising capacitance I 5 and the portion of resistance l6 above the variable point l8, which increases the high frequency response, is effective only when contact 9 is on the part of resistance 1 below tap 2l. The condenser I l and the lower part of resistance l6,

I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a source of audiofrequency currents. an impedance connected across said source having a tap, a utilization circuit connected between one side of said source and said nection from the ,other side 'of said source to a point variable along said resistance.

2. In combination, a source of audio frequency current, an impedance connected across said source having a tap, a utilization circuit connected between one side of said source and said tap, a condenser and a resistance connected in series between said oneside of said source and an intermediate point of said impedance, said condenser being adjacent said one side of said source, and a connection from the other side of said source ,to a pointvariable along said resistance.

3. In combination, asource of audio frequency currents, a first resistance connected across said source having. a tap, a load device connected between one terminal of said resistance and said tap, a second resistance and condenser connected in series between said one terminal and an intermediate point on said first resistance, and a connection from the opposite terminal of said first resistance to a point variable along said second resistance, said condenser being positioned between said second resistance and said one terminal and proportioned to by-pass currents of frequency high in the audio range when said variable point on said second resistance approaches the terminal connected to said condenser.

4. In combination, a source of currents having frequencies extending throughout the voice range, a potentiometer connected thereacross having output terminals one of which comprises a tap variable thereon, a resistance and a condenser connected in series-between an intermediate point on said potentiometer and the other of. said output terminals in the order mentioned and a. variable tap on said second resistance connected to the side of said source opposite saidother terminal, said condenser being proportioned to by-pass currents having frequency high in said range whereby movement of said variable tap afl'ects oppositely the extent to which said currents are'by-passed by said condenser and the extent to which they are supplied from said tap to said first resistance. v

5. In combination, a source of currents having awide range of audio frequencies, an impedance connected across said source, a load connected between one terminal of said impedance and a variable tap thereon, a resistance and a pair of condensers, said. resistance having one point thereon connected through one of said condensers to said one terminal and having another point connected through the other of said condensers to an intermediate point on said impedance, and

a connection from the opposite terminal of said impedance to a contact variable along said resistance between said two points thereon, whereby when said variable contact is at one of said points said one condenser forms a by-pass for high frequency currents across said source and said resistance impedes the flow of high fresource, a load connected between one terminal of said source and a tap variable on said impedance for volume control, and means to vary the degree to which high frequency currents are supplied from said source to said load, said means comprising a condenser, a resistance and a. secand condenser connected in series in that order between said first tap and said one terminal, and a connection from the other terminal of said source to a tap variable along said resistance whereby high frequency currents are alternatively by-passed across said source by th first of said condensers or transmitted to said first tap y said second condenser both in varying deareas in accordance with the variations in position of said second tap.

7. In combination, a source of voice or music frequencies, an impedance connected across said source, a load connected between one terminal of said source and a tap variabl on said impedance for volume control, and means to vary the degree to which high frequency currents are supplied from said source to said load, said means comprising a condenser, a resistance and a second condenser connected in series in that order between a second tap on said impedance and said one terminal and a connection from the other terminal of said source to a contact variable along said resistance, whereby high frequency currents are alternatively by-passed across said source by one of said condensers or transmitted to said second tap by the other of said condensers both in varying degrees in accordance with variations in the position of said contact, and an additional resistance and condenser connected in series between said second tap and said one terminal to by-pass high frequency currents.

WHLIAM s. BACHMAN. 

